Effect of functionally graded material (FGM) layers on the residual stress of polytypoidally joined Si₃N₄–Al₂O₃

Lee, Caroline S.,Ahn, Sung-Hoon,DeJonghe, Lutgard C.,Thomas, Gareth Elsevier 2006 Materials science & engineering. properties, micro Vol.434 No.1

<P><B>Abstract</B></P><P>A unique approach introducing sialon polytypoids as a functionally graded material (FGM) bonding has been used to join silicon nitride and alumina. The various multilayered FGM samples ranging from 3 to 20 layers were sintered to fabricate a crack-free joining of heterogeneous ceramics. To calculate thermal stresses for the various multilayered FGM samples, the finite element analysis program (FEAP) was used. These analyses results matched experimental results and showed why some samples had large residual stresses that resulted in fracture. Moreover, the electron probe X-ray microanalysis (EPMA) from a crack-free FGM sample had a smooth concentration profile, which verifies the interface diffusion during sintering at each graded layer and confirms a successful joining.</P>

Material Properties of Thick Aluminum Coating Made by Cold Gas Dynamic Spray Deposition

Lee, Jae Chul,Chun, Doo Man,Ahn, Sung Hoon,Lee, Caroline S. Trans Tech Publications, Ltd. 2007 Key engineering materials Vol.345 No.-

<P>Cold gas dynamic spray is a relatively new coating process by which coatings can be produced without significant heating during the process. Cold gas dynamic spray is conducted by powder sprayed using supersonic gas jet, and generally called the kinetic spray or cold spray. Its low process temperature can minimize the thermal stress and also reduce the deformation of the substrate. In this study, thick or macro scale deposition was studied while most researches on cold-spray have focused on micro scale coating. Measured material properties of macro scale deposition layer showed that elastic modulus and hardness were lower and electrical resistivity was higher than those of reference substrate material. The main causes of changed material properties were investigated by FE-SEM (Field Emission Scanning Electron Microscope) and EDS (Energy Dispersive X-ray Spectrometer) data. In this result, porous micro structure generated by imperfect plastic deformation might cause decrease in elastic modulus and hardness of the deposition layer by cold spray, and oxidized Al particles increased the electrical resistivity.</P>

Three Dimensional Analysis of Thermal Stress and Prediction of Failure of Polytypoidally Joined SI₃N₄-AL₂O₃ Functionally Graded Material (FGM)

Lee, Caroline S.,Kim, Sung-Geun,Ahn, Sung-Hoon,DeJonghe, Lutgard C.,Thomas, Gareth THE JAPAN INSTITUTE OF METALS 2007 MATERIALS TRANSACTIONS Vol.48 No.9

<P>Three-dimensional analysis methods to calculate residual stress for functionally graded material (FGM) sample using sialon polytypoids to join silicon nitride and Alumina are introduced in this paper. The various multilayered FGM samples with 3, 9, and 20 layers were sintered to fabricate a crack-free joining of heterogeneous ceramics. To calculate three-dimensional thermal stresses of those fabricated FGM samples, a finite element analysis tool, ALGOR, was used. The Von Mises failure criterion and the maximum stress criterion were applied to predict failures in the FGM samples. For each case, calculated strength of each FGM layer by rule of mixture was compared with predicted thermal residual stresses. The Von Mises failure criterion predicted the locations of cracks more precisely than the maximum stress criterion. Such analyses are especially useful for graded FGM samples where the residual stresses are very difficult to measure experimentally.</P>

Utility of Seated Lateral Radiographs in the Diagnosis and Classification of Lumbar Degenerative Spondylolisthesis

Issa Tariq Z.,Lee Yunsoo,Berthiaume Emily,Lambrechts Mark J.,Zaworski Caroline,Qadiri Qudratallah S.,Spracklen Henley,Padovano Richard,Weber Jackson,Mangan John J.,Canseco Jose A.,Woods Barrett I.,Kay 대한척추외과학회 2023 Asian Spine Journal Vol.17 No.4

Study Design: Retrospective cohort study.Purpose: Our goal was to determine which radiographic images are most essential for degenerative spondylolisthesis (DS) classification and instability detection.Overview of Literature: The heterogeneity in DS requires multiple imaging views to evaluate vertebral translation, disc space, slip angle, and instability. However, there are several restrictions on frequently used imaging perspectives such as flexion-extension and upright radiography.Methods: We assessed baseline neutral upright, standing flexion, seated lateral radiographs, and magnetic resonance imaging (MRI) for patients identified with spondylolisthesis from January 2021 to May 2022 by a single spine surgeon. DS was classified by Meyerding and Clinical and Radiographic Degenerative Spondylolisthesis classifications. A difference of >10° or >8% between views, respectively, was used to characterize angular and translational instability. Analysis of variance and paired chi-square tests were utilized to compare modalities.Results: A total of 136 patients were included. Seated lateral and standing flexion radiographs showed the greatest slip percentage (16.0% and 16.7%), while MRI revealed the lowest (12.2%, <i>p</i> <0.001). Standing flexion and lateral radiographs when seated produced more kyphosis (4.66° and 4.97°, respectively) than neutral upright and MRI (7.19° and 7.20°, <i>p</i> <0.001). Seated lateral performed similarly to standing flexion in detecting all measurement parameters and categorizing DS (all <i>p</i> >0.05). Translational instability was shown to be more prevalent when associated with seated lateral or standing flexion than when combined with neutral upright (31.5% vs. 20.2%, <i>p</i> =0.041; and 28.1% vs. 14.6%, <i>p</i> =0.014, respectively). There were no differences between seated lateral or standing flexion in the detection of instability (all <i>p</i> >0.20).Conclusions: Seated lateral radiographs are appropriate alternatives for standing flexion radiographs. Films taken when standing up straight do not offer any more information for DS detection. Rather than standing flexion-extension radiographs, instability can be detected using an MRI, which is often performed preoperatively, paired with a single seated lateral radiograph.

How Does the Severity of Neuroforaminal Compression in Cervical Radiculopathy Affect Outcomes of Anterior Cervical Discectomy and Fusion

Lambrechts Mark J.,Issa Tariq Z.,Lee Yunsoo,Tran Khoa S.,Heard Jeremy,Purtill Caroline,Fried Tristan B.,Oh Samuel,Kim Erin,Mangan John J.,Canseco Jose A.,Kaye I. David,Rihn Jeffrey A.,Hilibrand Alan S 대한척추외과학회 2023 Asian Spine Journal Vol.17 No.6

Study Design: This study is a retrospective cohort study.Purpose: This study aims to determine whether preoperative neuroforaminal stenosis (FS) severity is associated with motor function patient-reported outcome measures (PROMs) following anterior cervical discectomy and fusion (ACDF).Overview of Literature: Cervical FS can significantly contribute to patient symptoms. While magnetic resonance imaging (MRI) has been used to classify FS, there has been limited research into the impact of FS severity on patient outcomes.Methods: Patients undergoing primary, elective 1–3 level ACDF for radiculopathy at a single academic center between 2015 and 2021 were identified retrospectively. Cervical FS was evaluated using axial T2-weighted MRI images via a validated grading scale. The maximum degree of stenosis was used for multilevel disease. Motor symptoms were classified using encounters at their final preoperative and first postoperative visits, with examinations ≤3/5 indicating weakness. PROMs were obtained preoperatively and at 1-year follow-up. Bivariate analysis was used to compare outcomes based on stenosis severity, followed by multivariable analysis.Results: This study included 354 patients, 157 with moderate stenosis and 197 with severe stenosis. Overall, 58 patients (16.4%) presented with upper extremity weakness ≤3/5. A similar number of patients in both groups presented with baseline motor weakness (13.5% vs. 16.55, <i>p</i> =0.431). Postoperatively, 97.1% and 87.0% of patients with severe and moderate FS, respectively, experienced full motor recovery (<i>p</i> =0.134). At 1-year, patients with severe neuroforaminal stenosis presented with significantly worse 12-item Short Form Survey Physical Component Score (PCS-12) (33.3 vs. 37.3, <i>p</i> =0.049) but demonstrated a greater magnitude of improvement (Δ PCS-12: 5.43 vs. 0.87, <i>p</i> =0.048). Worse stenosis was independently associated with greater ΔPCS-12 at 1-year (β =5.59, <i>p</i> =0.022).Conclusions: Patients with severe FS presented with worse preoperative physical health. While ACDF improved outcomes and conferred similar motor recovery in all patients, those with severe FS reported much better improvement in physical function.

국외논문정보 - 캐나다의 장기 교대작업에 의한 유방암 발생위험도 증가

Grundy, Anne,Richardson, Harriet,Burstyn, Igor,Lohrisch, Caroline,SenGupta, Sandip K,Lai, Agnes S,Lee, Derrick,Spinelli, John J,Aronson, Kristan J 대한산업보건협회 2016 산업보건 Vol.343 No.-

Evaluation of morphological architecture of cellulose chains in grass during conversion from macro to nano dimensions

Pandey, Jitendra K.,Kim, Chung-Soo,Chu, Won-Shik,Lee, Caroline S.,Jang, Dong-Young,Ahn, Sung-Hoon De Gruyter 2009 E-Polymers Vol.9 No.1

<P><B>Abstract</B></P><P>The cellulose nanowhiskers (CNW) are of imminent importance in the development of ecofriendly green material for environment. Morphological study of their structure was carried out after extraction from grass. The controlled alkali and acid hydrolysis after soxhlet extraction of bleached fiber in ethanol and water provided a mixture of micro/nano fiber which can be further converted into CNW by mechanical treatment. Width of obtained CNW were found to be ~10-65 nm with length of several nanometers as evidenced by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The changes in dimensions during alkali treatment, bleaching and acid hydrolysis of grass exhibited an interesting architecture and clarify the phenomenon of separation of nano level fibrils from the matrix of hemicellulose and lignin which starts after swelling of fibers and opening from middle followed by splitting from each other. The nanofibers were embedded in the matrix surrounded by amorphous layers. The size of fibers was directly associated with the extent of treatments. The crystalline part of fiber was intact during hydrolysis which must be attributed to easy removal of amorphous region by penetration of hydronum ions from acid. The results of SEM and TEM were correlated with the Scanning Ion Microscopy (SIM) which showed a direct evidence of breaking of thick fiber strands resulting in the formation of sharp edged crystalline entities composed of cellulose crystals.</P>

FABRICATION OF FLEXIBLE DYE SENSITIZED SOLAR CELL USING LASER ASSISTED NANO PARTICLE DEPOSITION SYSTEM

Jung Oh Choi,Chung Soo Kim,Gil Yong Lee,Hyun Taek Lee,Jae Il Park,Caroline S. Lee,Sung Hoon Ahn 한국신재생에너지학회 2012 AFORE Vol.2012 No.-

Electrical and electrochemical migration characteristics of Ag/Cu nanopaste patterns.

Koh, Minkwan,Kim, Kwang-Seok,Park, Bum-Geun,Jung, Kwang-Ho,Lee, Caroline S,Choa, Yong-Ho,Jeong, Myung Yung,Jung, Seung-Boo American Scientific Publishers 2014 Journal of Nanoscience and Nanotechnology Vol.14 No.12

<P>Since direct printing technology has developed intensively, low-cost fabrication and reliability have become critical challenges for mass production of printed electronic devices. The silver/copper (Ag/Cu) nanopaste was manufactured by Ag nanopaste mixed with different proportions of Cu nanoparticles ranging from 0 to 5 vol.% in order to investigate the influences of Cu content on the electrical properties and electrochemical migration (ECM) characteristics. The patterns were constructed on a glass wafer via screen printing with the Ag/Cu nanopaste. They were then annealed through debinding for 30 min in air followed by sintering for 30 min in a hydrogen atmosphere at various temperatures (150, 200, 250, and 300 degrees C). The electrical resistivity of printed patterns that were sintered at 150 degrees C grew with increases in the percentage of Cu content in the Ag/Cu nanopaste, while printed patterns that were sintered at 300 degrees C show similar electrical resistivity values of around 2-3 μω cm regardless of Cu content. The ECM characteristics of the printed patterns were evaluated by performing a water drop test. The printed patterns that were sintered at higher temperatures showed longer ECM times. At 300 degrees C, the ECM time was considerably lengthened when the Cu content was over 2 vol.%, and the 5 vol.% Cu pattern showed the longest ECM time of 305 s, which was around 1.65 times that of the Ag pattern.</P>

<i>In situ</i> reduction and exfoliation of g-C₃N₄ nanosheets with copious active sites <i>via</i> a thermal approach for effective water splitting

Pawar, Rajendra C.,Kang, Suhee,Han, Hyuksu,Choi, Heechae,Lee, Caroline S. The Royal Society of Chemistry 2019 Catalysis Science & Technology Vol.9 No.4

<P>Poor optical absorbance and charge recombination are the major drawbacks of polymeric graphitic carbon nitride (g-C3N4)-based photocatalysts. In this paper, we show for the first time a single-step <I>in situ</I> technique to control the porosity of two-dimensional g-C3N4 sheets and exfoliate them by introducing ascorbic acid (AA) molecules. The AA simultaneously acts as the carbon (C) source and deposits amorphous C onto g-C3N4 sheets. Nanosized pores are also introduced into the g-C3N4 sheets, leading to a large number of active sites. The as-prepared C-doped porous g-C3N4 nanosheets demonstrate a high visible light-photocatalytic H2 production activity of 793 μmol g<SUP>−1</SUP> with the optimum structure, which is almost 25 times higher than the value obtained with bulk g-C3N4 (31 μmol g<SUP>−1</SUP>). This exceptional photocatalytic performance arises from the C-doped conjugated system and porous nanosheets. The enhanced photocatalytic H2 evolution was attributed to the effective separation and transport of charge carriers by the deposition of C onto the nanosheets and an increased number of active sites resulting from the nanopores created inside the g-C3N4 sheets. Moreover, molecular dynamics (MD) simulations confirm that the interaction between AA and melamine molecules at elevated temperatures results in the formation of C-doped porous and exfoliated g-C3N4 structures. Therefore, the present approach is very promising for application to the design of new and efficient photocatalysts for photocatalytic H2 evolution under visible irradiation.</P>